Substructures and density profiles of clusters in models of galaxy formation

In this paper we investigate, using high resolution N-body simulations, thedensity profiles and the morphologies of galaxy clusters in seven models ofstructure formation. We show that these properties of clusters are closelyrelated to the occurrence of a significant merging event in the recent past.The seven models are: (1) the standard CDM model (SCDM) with $\Omega_0 = 1$,$\Lambda_0=0$ and $h=0.5$; (2) a low-density flat model (FL03) with$\Omega_0=0.3$, $\Lambda_0=0.7$ and $h=0.75$; (3) an open model (OP03) with$\Omega_0=0.3$, $\Lambda_0=0$ and $h=0.75$; (4) a low-density flat model (FL02)with $\Omega_0=0.2$, $\Lambda_0=0.8$ and $h=1$; (5) an open model (OP02) with$\Omega_0=0.2$, $\Lambda_0=0$ and $h=1$; (6) a low-density flat model (FL01)with $\Omega_0=0.1$ and $\Lambda_0=0.9$; (7) an open model (OP01) with$\Omega_0=0.1$ and $\Lambda_0=0$. We find that the density profiles andmorphologies of clusters depend both on $\Omega_0$ and on $\Lambda_0$. For$\Lambda_0=0$, these properties are a monotonic function of $\Omega_0$.Clusters in OP01 have the steepest density profiles, their density contours arethe roundest and show the smallest center shifts. The other extreme case isSCDM, where clusters show the least steep density profiles and the mostelongated contours. For a given $\Omega_0$ ($<1$), clusters in the flat model(i.e. with $\Lambda_0=1-\Omega_0$) have flatter density profiles and lesssubstructures than in the corresponding open model. In particular, our resultsshow that low-density flat models with $\Omega_0\sim 0.3$, which are currentlyconsidered as a successful alternative to SCDM, can produce a substantialfraction of clusters with substructures. This is in contrast to the conceptionthat this kind of models may have serious problem in this aspect.Comment: 20 pages, uuencoded compressed tar ps-file, including tables. 8 figures not included. The figures can be obtained by anonymous ftp at: ftp://ibm-3.mpa-garching.mpg.de/pub/jing/jmbf941_fig.tar.Z The compressed tar ps-file of the text is also available at: ftp://ibm-3.mpa-garching.mpg.de/pub/jing/jmbf941_paper.tar.